- Canis Major Dwarf Galaxy
name = Canis Major Dwarf
type = Irr
ra = RA|07|12|35.0cite web
title=NASA/IPAC Extragalactic Database
work=Results for Canis Major Dwarf
dec = DEC|-27|40|00
dist_ly = 25,000 ly
size_v = 12 degrees × 12 degrees
constellation name =
notes = -
names = CMa Dwarf
The Canis Major Dwarf galaxy is located in the same part of the sky as the
constellationof Canis Major. The galaxycontains a relatively high percentage of red giant stars, and is thought to contain an estimated one billion stars in all.
The Canis Major
dwarf galaxyis classified as an irregular galaxyand is now thought to be the closest neighbouring galaxy to our location in the Milky Way, being located about 25,000 light-years away from our Solar SystemFact|date=February 2007 and 42,000 light-years from the Galactic Center. It has a roughly elliptical shape and is thought to contain as many stars as the Sagittarius Dwarf Elliptical Galaxy, the previous contender for closest galaxy to our location in the Milky Way.
The galaxy was first discovered in November 2003 by an international team of French, Italian, British and Australian
astronomers. Although closer to the Earththan the centre of the galaxy itself, the Canis Major Dwarf galaxy was difficult to detect as it is located behind the plane of the Milky Way, where concentrations of stars, gas and dust are densest. This, along with its small size, explains why it was not discovered sooner.
The team of astronomers that discovered it were collaborating on analysis of data from the Two-Micron All Sky Survey (2MASS), a comprehensive survey of the sky in
infraredlight, which is not blocked by gas and dust as severely as visible light. Because of this technique, scientists were able to detect a very significant over-density of class M giant stars in a part of the sky occupied by the Canis Major constellation, along with several other related structures composed of this type of star, two of which form broad, faint arcs.
Astronomers believe that the Canis Major Dwarf Galaxy is in the process of being pulled apart by the
gravitational fieldof the more massive Milky Way galaxy. The main body of the galaxy is extremely degraded. Tidal disruption causes a long filament of stars to trail behind it as it orbits the Milky Way, forming a complex ringlike structure sometimes referred to as the Monoceros Ringwhich wraps around our galaxy three times. The stream of stars was first discovered in the early 21st century by astronomers conducting the Sloan Digital Sky Survey. It was in the course of investigating this ring of stars, and a closely spaced group of globular clusterssimilar to those associated with the Sagittarius Dwarf Elliptical Galaxy, that the Canis Major dwarf galaxy was discovered.
Globular clusters thought to be associated with the Canis Major Dwarf galaxy include
NGC 1851, NGC 1904, NGC 2298and NGC 2808, all of which are likely to be a remnant of the galaxy's globular cluster system before its "accretion", or swallowing, into the Milky Way. NGC 1261is another nearby cluster, but its velocity is different enough from that of the others to make its relation to the system unclear. The Canis Major Dwarf galaxy may also have associated open clusters, including Dol 25and H18, and possibly AM-2. It is thought that the open clusters may have formed due to the dwarf galaxy's gravity perturbing material in the galactic diskand stimulating star formation.
The discovery of the Canis Major Dwarf Galaxy and subsequent analysis of the stars associated with it has provided some support for the current theory that galaxies may grow in size by swallowing their smaller neighbors. Martin et al. believe that the preponderance of evidence points to the accretion of a small
satellite galaxyof the Milky Way which was orbiting roughly in the plane of the galactic disk.
A new study by
Yazan Momanyusing 2MASS data casts doubts on the nature of the dwarf galaxy. The data suggests that the trail of stars is actually part of the warped galactic disc. This conclusion, however, is still being challenged and the true nature of the overdensity in Canis Majorremains unknown.Fact|date=June 2007
Galaxy formation and evolution
* N. F. Martin, R. A. Ibata, M. Bellazzini, M. J. Irwin, G. F. Lewis, W. Dehnen, (February 2004). [http://xxx.lanl.gov/abs/astro-ph/0311010 A dwarf galaxy remnant in Canis Major: the fossil of an in-plane accretion onto the Milky Way.] "Monthly Notices of the Royal Astronomical Society" 348 (1) 12.
* [http://astro.u-strasbg.fr/images_ri/canm-e.html Official press release announcing discovery (University of Strasbourg)]
* [http://www.seds.org/messier/more/cma_dw.html SEDS page on the Canis Major dwarf galaxy]
* [http://www.skynightly.com/reports/Deriving_The_Shape_Of_The_Galactic_Stellar_Disc.html Deriving The Shape Of The Galactic Stellar Disc] (SkyNightly) Mar 17, 2006
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